Cenozoic Tectonic Deformation Along the Pontarlier Strike‐Slip Fault Zone (Swiss and French Jura Fold‐and‐Thrust Belt): Insights From Paleostress and Geomorphic Analyses

Abstract

AbstractWe present insights into the Cenozoic tectonic evolution of the region around the Pontarlier strike‐slip fault zone within the Jura fold‐and‐thrust belt by combined study of paleostress and geomorphic analyses. A preliminary separation of heterogeneous fault‐slip data and bedding‐tilt correction was performed before determining the paleostress axes orientations. The paleostress results provide evidence of multiphase deformation history consisting of four successive events. These events include a strike‐slip stress regime with ∼N‐S directed compression, a NW‐SE directed extensional stress regime, a NW‐SE trending compressional stress regime, and a strike‐slip stress regime with a mean NW‐SE directed compression. The directions of extension and compression for the second and third events are consistent with the general direction of maximum horizontal far‐field stress near the northern segment of the Pontarlier fault and generally deviate from those found near the southern segment.Geomorphic analysis of selected rivers along the southern segment of the Pontarlier fault, together with sub/surface geological observations provides new clues on Late Cenozoic strike‐slip reactivation of inherited extensional structure of Mesozoic age. These clues include (i) anomalous zones of high gradient within uniform bedrock lithology that spatially coincide with an obvious change in the depth to top Mesozoic layers; and (ii) right‐lateral offset of river channels, which is consistent with NW‐SE compression related to the youngest paleostress and current stress field. A combination of paleostress and geomorphic analyses provides a useful complementary approach for unraveling the Cenozoic tectonic evolution of the region characterized by a general lack of outcrop of Cenozoic rocks.